Transparent bulk Co2+ : ZnAl2O4/SiO2 nanocomposites containing nanocrystalline Co2+ : ZnAl2O4 dispersed in silica glass matrix were obtained by the sol-gel method. The gels of composition 89SiO(2)-6Al(2)O(3)-5ZnO-xCoO (x = 0.2, 0.4, 0.6, 0.8, 1.0) (mol%) were prepared at room temperature by using two different aluminum salts, aluminum nitrate and aluminum alkoxide (aluminum-iso-propoxide, Al(OPri)(3)), as starting materials. The transparent gels were converted to the crystalline phase of gahnite by heating above 900 degrees C. The microstructural evolution of gels was characterized. The effect of CO2+ concentration on spectroscopic properties was also discussed. Co2+ : ZnAl2O4 nanocrystals dispersed in the SiO2-based glass are formed at lower heat-treatment temperature and shorter heating time by using Al(OPri)(3) as raw material.